Various ladder extensions have been proposed for this purpose in the past, as taught, for example, by U.S. Pat. No. 442,360, issued Dec. 9, 1890 to M. F. Coomes; U.S. Pat. No. 1,419,748, issued June 13, 1922 to L. M. Miller; U.S. Pat. No. 2,320,144, issued May 25, 1943 to E. Johnson; U.S. Pat. No. 2,481,581, issued Sept. 13, 1949 to E. Ehnhuus; U.S. Pat. No. 3,484,814, issued Dec. 19, 1969 to J. F. Meehan; U.S. Pat. No. 3,882,966, issued May 13, 1975 to Osvaldo Fasano and U.S. Pat. No. 4,412,599 issued Nov. 1, 1983 to Edward McCrudden et al. However, these prior ladder extensions have either had the disadvantage of being made of relatively expensive metal components and/or requiring such components to be provided on a metal ladder, or have had the disadvantage of relying on friction between the extension and a leg of the ladder to counteract displacement of the ladder leg relative to the extension in response to weight on the ladder.